A lithium secondary cell is excellent in the energy density, the output density etc., and its downsizing and weight reduction are possible, and thus its demand is rapidly increasing as a power source for a portable device such as a notebook computer, a mobile telephone or a handy video camera. A lithium secondary cell attracts attention also as a power source for e.g. an electric automobile or load leveling of the electric power.
A positive electrode employed in a lithium secondary cell is constituted usually by a current collector and a positive electrode active material layer formed on the surface of the current collector, containing a positive electrode active material, an electrically conductive material and a binder. As the positive electrode active material, a compound oxide of lithium and a transition metal, such as lithium/manganese compound oxide, lithium/cobalt compound oxide or lithium/nickel compound oxide, attracts attention since high performance cell characteristics can be obtained. A lithium secondary cell employing such a lithium-based compound oxide has such advantages that a high voltage can be obtained, and that a high output can be obtained.
A layered lithium-nickel-based compound oxide powder as a positive electrode material for a lithium secondary cell is produced usually by spray drying a material slurry containing a lithium material, a nickel compound and a transition metal element compound, and firing the obtained dried particles. Heretofore, in production of a lithium-nickel-based compound oxide powder by this spray drying method, the viscosity of the material slurry is an important factor, and if the viscosity of the material slurry is excessively low taking ejectability from a spray nozzle into consideration, spherical particles are less likely to be formed, and if the viscosity is too high, the nozzle is likely to be clogged. Accordingly, the viscosity of the material slurry is usually set to from 200 to 1000 cp. Further, in view of the industrial productivity and prevention of clogging of the nozzle, the gas supply amount at the time of spray drying is set to be considerably in excess relative to the slurry. In spray drying employing a material slurry having the above-described viscosity, the ratio of the gas supply amount G (L/min) to the slurry supply amount S (g/min), G/S (gas/slurry ratio) is set to at least 5 so that the gas amount is considerably in excess.